Optical mount with UV adhesive and protective layer

Abstract

An assembly includes a holder (5), an optical component (1) transmitting radiation in a first region of ultraviolet (UV) radiation adhered to the holder by an adhesive (4), the adhesive being hardenable by radiation of a second region of ultraviolet radiation, a first layer (3) disposed between the optical component and the adhesive, and a second layer (2) for enhancing adhesion between the optical component and the first layer. The first layer is capable of transmitting radiation of the second region of UV radiation and obstructing to a high degree transmission of UV radiation of the first region by at least one of absorption and reflection. The optical component has a transmitting zone and the first layer is located outside of the transmitting zone. The second layer for enhancing adhesion between the optical component and the first layer is disposed between the first layer and the optical component. The assembly can be used, for example, in an illumination system and / or a projection system of a microlithography projection apparatus.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates to an assembly including a holder—in particular, a mount—and an optical component adhered to the holder by an adhesive, wherein the optical component is suitable for transmitting radiation in a first region of ultraviolet (UV) radiation, and wherein the adhesive is hardened by UV radiation in a second region of ultraviolet radiation, the adhesive being protected from radiation of the first region of ultraviolet radiation by an adhesive-protecting layer. [0003] 2. Description of the Related Art [0004] Japanese Patent Application JP 8-72300 provides an example of an assembly with an ultraviolet curable adhesive. Such assemblies form, among other things, mounted lenses and the like of illumination systems and projection systems for microlithography. [0005] Japanese Patent Application JP 11-014876 describes a protective member for shielding the surface of the adhesive of such an assembly from ultra...

AI Technical Summary

Benefits of technology

[0012] In one embodiment of the invention, a thermal expansion coefficient of the second, adhesion-enhancing layer is closer to a thermal expansion coefficient of the optical component than to a thermal expansion coefficient of the first, adhesive-protecting layer. Thermal expansion coefficients of fluoride materials used for optical components transmitting below 300 nm lie typically in a range of about 10−5 / K. Thermal expansion coefficients of oxide materials which are preferably used for the adhesive-protecting layer lie typically in a range of about 10−6 / K. By choosing the thermal expansion coefficient of the adhesion-enhancing layer closer to the range of values of fluoride materials than to the range of values of oxide materials, a good thermal stability of the adhesion between the optical component and the adhesion-enhancing layer is ensured.

[0013] In one embodiment of the invention, the optical component is composed of a first fluoride material, in particular CaF2, and the adhesion-enhancing layer is, at least in a zone adjacent to the optical component, composed of a second fluoride material, particularly one of MgF2, LaF3, GdF3, NdF3, AlF3, cryolite, chiolite, CeFx, YFx, or mixtures thereof. Material properties of the adhesion-enhancing layer and the optical component are similar due to the fact that both are consisting of fluoride materials and therefore sufficient tensile strength between the two is assured.

[0016] A continuous change of composition between the first and the second material can be advantageously accomplished by a process of ion mixing. During this process, the surface of the first material is irradiated with ions while a deposition of the second material on the first material is taking place, e.g. by physical vapor deposition. As a result, ions of the second material and / or ions of a third material, for example ions of an inert gas, are accumulated inside of the first material on a length ranging from the surface of the material to the maximum ion penetration depth, thereby forming an ion mixing layer. By adjusting the kinetic energy of the irradiating ions it is possible to adjust the thickness of the ion mixing layer.

[0020] Coating of the first and / or second layer can be performed by at least one thin film process such as vapor deposition, sputtering, physical vapor deposition (PVD), spraying, chemical vapor deposition (CVD), ion assisted deposition (IAD), plasma enhanced chemical vapor deposition (PECVD), spincoating or another deposition technique. It can be particularly advantageous to combine the processes of physical vapor deposition or chemical vapor deposition with ion assistance.

[0021] An optical component according to the invention has a transmitting zone and a surface arranged outside of the transmitting zone, the surface being coated by a second layer, the second layer being coated by a first layer suitable for protecting the adhesive from radiation in a first region of ultraviolet (UV) radiation transmitted by the optical component during use of the optical component, the second layer being adapted for enhancing adhesion between the optical component and the first layer. The optical component can be adhered to a holder with an adhesive, to form a mechanically stable assembly.

Problems solved by technology

It has been found that the known mount adhesives based on epoxy resin, which can be hardened with UV radiation of a region consisting only of wavelengths larger than 300 nm and including an Hg-I line at 365 nm, can be considerably damaged by irradiation with UV radiation from the deep UV region, in particular at about 248 nm, 193 nm or 157 nm.

UV absorbing fillers in the adhesive mass do not prevent failure of the boundary layer of the adhesive adjacent to the optical component.

Material properties of optical components transparent for UV radiation may differ considerably from material properties of the adjacent protective layer, a circumstance which may cause the tensile or compression strength between the two to be insufficient to assure long term stability of the mechanical bond between the optical component and the holder.

Images